Side Effects
by waitingfox22
Summary: A villain makes it into the school, though their attack is quickly dealt with and no harm seems to be done. Save for the fact no one had any idea what the villain's Quirk was. Too bad no one will know until the side effects hit them the next day. Drabble-Fic involving Midoriya and Bakugou dealing with all kinds of different "side effects".
1. Body Swap

Disclaimer: My Hero Academia is not mine, nor do I own the characters.

Warnings: Cursing, OOC-ness, possible spoilers, a bt of shonen-ai, etc.

* * *

It had happened out of the blue. A villain had made her way through U.A.'s security and was running amuck. Being the heroes-in-training they were, Izuku and Katsuki went in right away to deal with the villain. Already All Might and Eraser Head had caught the villain into a corner.

"Stay back kids, you shouldn't be here." Eraser Head growled when the boys had made it to his side. The villain let out a laugh, a hand coming up to cover her mouth.

"This is just perfect." She purred.

"That is enough." All Might put his hands to his hips and stood tall, "Stand down and just turn yourself in." The villain pouted.

"Fine, fine." She whined, which caught everyone off guard, "But not before I do this!" She then jumped right towards Izuku and Katsuki. Her hands grabbed their heads and she caused them to butt heads. She also did the same to All Might and Eraser Head before she was grabbed by the arm. From there the villain did give in. She had a smile plastered on her face as she was taken away.

"That was weird." Izuku muttered as he rubbed his sore forehead.

"Shut the fuck up Deku." Katsuki hissed as he did the same action.

"I guess we should end the school day early…" Eraser Head muttered.

"Agreed, I shall speak with the principal." All Might nodded his head. With that the school was released as easy as it was stated. By the time Izuku got home, he was all kinds of tired. Not only did his head hurt from the fight, but his mind was on overdrive as he tried to think of what the villain's plan was and what her Quirk could have been. He was a zombie while he ate, and just wanted to go straight to bed afterwards.

"Oh dear, I hope you're not getting sick Izuku…" Mrs. Midoriya whimpered as she watched her son put away his dishes.

"I don't know mom…I wanna go to bed though." At that Izuku had let out a big yawn and he rubbed at his eyes.

"Okay, just let me know if you need anything." Mrs Midoriya squeaked. Izuku nodded to his mom before heading to his bedroom. He changed into his pjs and just told himself that he'd shower in the morning. But just before he was going to pull up his covers, he heard the buzzing of his phone. Grabbing the cell, Izuku checked what was up.

 _Heard that you were in the fight. Are you alright? - Shouto_

Izuku did smile at the text. He sometimes forgot at how much of a worry-wort Shouto could be.

 _I'm fine Shouto. I'm really tired, but fine. All that happened was the villain made Kacchan and I headbutt one another. - Self_

It didn't take very long for Shouto to reply.

 _If you believe that everything is fine I will trust your judgement. See you tomorrow. - Shouto_

Izuku smiled as he sent back an agreement and put his phone aside for the night. With his happy thoughts, Izuku went to sleep, unaware that with that the villains Quirk finally came into effect.

When morning came around Izuku knew immediately that something was very, very wrong. He sat up with a jolt and looked all around; the room he was in was completely unfamiliar to him. Though all it took for things to click into place was for Izuku to look down at his hands. First of all, what he saw where not his own hands, but he did know exactly whose they were. With a small whimper Izuku's face began to pale; well it wasn't his face but Izuku could tell it was going pale. He was in Katsuki Bakugou's body. What was he going to do?!

On the other hand, Katsuki was just as freaked the fuck out. He was currently in Izuku's body and very pissed at the world. He decided to glare at Izuku's phone as he tried to think of something to do.

"Izuku, is everything alright? You're going to late for school if you don't get ready soon." Mrs. Midoriya's worried voice came from outside the room from the other side of the door.

"Oh shit, how the fuck am I supposed to act like fucking Deku?" Katsuki grumbled under his breath and swung his legs (well technically they were Izuku's) over the side of the bed. As he stood Katsuki couldn't help but make a comment about Izuku's shortness and went on a search for Izuku's school uniform. As much as Katsuki hated this situation, he knew that the only he was seeing his own body would be at school; most likely with Izuku inside it.

"Deku better not be fucking things up on his end." Katsuki growled under his breath as he peeked out the doorway. In the hall he spotted Mrs. Midoriya. Now how was he getting past her without causing suspicion?

"Were you up late talking to Todoroki again Izuku? I thought I told you to pay more attention to the clock. Well…go on and get to school dear." Mrs. Midoriya gave a small sigh and stepped out of the way.

"Uh…" Katsuki didn't know what to say, and what was this about the Half-and-Half? In the end Katsuki had just given Mrs. Midoriya a wave and that had seemed to work. From there he ran off to U.A. On the way there, Izuku's phone started buzzing. Having felt go off enough times Katsuki decided to answer it. And note it was way too easy to figure out Izuku's password.

 _Kacchan! - Unknown Number_

 _We switched bodies! This is so weird! - Unknown Number_

 _I guess I'll see you at school? - Unknown Number_

 _Kacchan? - Unknown Number_

Katsuki snorted as he read all the messages before he decided to finally reply back.

 _We are going straight to fucking Recovery Girl you here me Deku? And you better not be screwing things over for me! - Self_

It took only seconds for Izuku to reply with a 'Understood' and Katsuki shoved the cell phone back into his pocket. Once at the school Katsuki was surprised at the lack of students that were around. But he just brushed it aside, the less people the less they knew of him being stuck in Izuku's body.

"Izuku!" Katsuki froze when he heard Shouto call out to him. "Feeling better from last night?" Shouto quickly made his way to Katsuki's side. Katsuki could only stare at Shouto in shock. Just what was going on? And for how long were Deku and the Half-and-Half on a first name basis?

"S-Shouto?" Katsuki uncharacteristically stuttered out.

"You don't sound very well. Maybe you should just head back home? I'm sure your mother would understand." Shouto brought a hand up to cup Katsuki's (but really Izuku's) face. Katsuki was dumbfounded. He couldn't move. He wanted to lash out and curse to high heaven, but deep down he still didn't want to blow his cover. Just as Shouto started to lean in, perhaps for a kiss, Katsuki felt the urge to finally push him off. His hand twitched with a power he knew was not his own and he began to worry once again.

"Don't!" A familiar voice shouted down the hall. Shouto paused and looked up with a glare. The Half-and-Half even moved so that he stood protectively over Katsuki.

"What do you want Bakugou?" Shouto growled and wrapped a hand around Katsuki's waist.

"Stop, don't you do anything to him!" Izuku (in Katsuki's body of course) shouted and shook his head. It was evident that Shouto was confused with how, in his eyes Katsuki, was acting and he slowly calmed down.

"Why? You've never been nice to him before and who are you tell me what to do with my boyfriend?" Shouto huffed out while still staring at Izuku. Now Katsuki was done, he did not want to deal with this weird ass situation any longer.

"Fuck! Get off me Halfy and Deku what the fuck?" Katsuki lashed out and pushed Shouto away from him. Shouto was obviously shocked at the outburst.

"K-Kacchan watch your language!" Izuku whined, which only seemed to make Katsuki angrier.

"You better have not made me seem like a pussy in front of my parents." Katsuki growled.

"What is going on here?" Shouto jumped back into the conversation. Izuku bowed his head and pouted (which looked totally weird on Katsuki's face).

"Oh Shouto…somehow Kacchan and I switched bodies this morning. We were supposed to be going to see Recovery Girl right now." Izuku whimpered out.

"Cut that out!" Katsuki fought back the urge to hit Izuku. Now it came time for Shouto to blush.

"I'm sorry." Shouto murmured and started to scratch at his cheek.

"Bakugou, Midoriya!" Everyone's attention was brought to see Mr. Aizawa.

"I guess we'll talk later…Good luck?" Shouto decided it was time for him to go off to class. This left Katsuki, Izuku, and Mr. Aizawa alone in the hallway.

"To Recovery Girl with you boys." Mr. Aizawa sighed.

"Um…" Izuku wanted to question his teacher. He clearly remembered that yesterday not only had he and Katsuki smash heads, but Mr. Aizawa and All Might had as well. And well if this was the result of a Quirk…then they could be switched as well.

"Stop right there my boy. That's definitely Midoriya in there." Mr. Aizawa shook his head and put a hand on Izuku's (Katsuki's) shoulder.

"You got switched up too?" Katsuki snorted slightly.

"Bakugou now is not the time." All Might (though it was Mr. Aizawa's body) waved a hand in gesture to be followed. The boys followed their teacher without a second thought. Once in the Nurse's Office, Recovery Girl went right to work on checking everyone out. Though during his check-up Katsuki couldn't help but ask where All Might was.

"Shouldn't Mr. Aizawa be here in All Might's body?" Katsuki huffed.

"He's already been checked and in the next room over. Think nothing of it." Recovery Girl hummed as she continued to work.

"So uh, you got any idea if this is Quirk related or not?" Izuku was sitting on a bed and kicking his legs back and forth.

"It is, and from the looks of things it should wear off in a matter of hours." Recovery Girl patted Katsuki's hand and smiled.

"Hours?" Katsuki growled and clenched his hands into fists.

"It'll be fine Kacchan…" Izuku shook his head and turned to Recovery Girl, "Should we just stay here then?"

"It'd be best. I say you just sleep things off okay dears?" Recovery Girl gave a nod and stepped away from Katsuki.

"Fine." Katsuki rolled his eyes and crossed his arms over his chest.

"Keep a good eye on them ma'am." All Might gave Recovery Girl a wave before going off. Izuku figured he was going to go be Mr. Aizawa. With all that Recovery Girl went to her desk to deal with paperwork as Izuku and Katsuki sat in beds that were right next to one another. In a surprising moment, Katsuki was the one to break the room's silence.

"For how long have you and Half-and-Half dating?" Katsuki slightly grumbled. Izuku's face warmed and he turned his head away. Katsuki had made sure to snap a nasty comment his way while Izuku took his time to reply.

"It was a few weeks after the Sports Festival okay?" Izuku finally spoke out.

"Seriously? I can't believe I never fucking noticed." Katsuki brought a hand up to rub at his chin. Izuku gave a little laugh, which was totally weird since it technically was coming from Katsuki, and smiled over to Katsuki.

"I guess you don't know me as well as you thought. It wouldn't be the first time." Izuku pointed out.

"Shut up Deku!" Katsuki growled and raised his hands up for a fight.

"Careful! You don't want to go activating my Quirk." Izuku squeaked.

"Tsk…" Katsuki knew that, he didn't want to break any bones, even if they were Izuku's, "Speaking of Quirks, how the fuck have you not been blowing shit up?"

"Oh, well. I've just kinda been making sure not to get my…your hands all sweaty. I've done a few small bursts on accident, but no harm no foul." Izuku replied. Katsuki huffed, of course Izuku understood how his Quirk worked. Damned nerd was always sticking his nose into everyone's Quirks and business.

"I just want out of your stupid body already." Katsuki gave in to a whine.

"Agreed! I can't believe Shouto almost kissed you!" Izuku huffed out.

"Don't talk about that! Boyfriend or not I was going to punch the daylights out of him!" Katsuki growled.

"Kacchan!" Izuku whined. For the next handful of minutes the boys made small talk and arguments. It was Recovery Girl that finally told them to hush up and actual try to take naps. Izuku, being the goodie-goodie he was, was quick to listen to the medical hero and made himself comfortable in the bed. Meanwhile it took some piss and vinegar to get Katsuki to attempt a nap.

"If we aren't back in our own bodies when I wake up, I gonna kill you." Katsuki grumbled out loud before trying to get some shut eye. Luckily the little spitfire got his wish. He left the Nurse's Office in his own body, leaving Izuku behind.

"That was weird, but it could have been worse." Izuku chuckled to himself as he helped Recovery Girl tidy up her office.

"Take care." Recovery Girl hummed when Izuku left. By this time school was out, so Izuku was heading straight home. Along the way he pulls out his phone and sends a text to Shouto.

 _How was today?_

 _P.S. I'm back to normal! Sorry about this morning! - Self_

It hadn't taken very long for Shouto to reply.

 _Lady Midnight took over Homeroom in place of Mr. Aizawa and Snipe had taken over for All Might. I'll be sure to send you today's notes later tonight. As for the other thing, you owe me. - Shouto_

 _I figured. You're the best Sho! Love you! - Self_

 _Love you too. - Shouto_

Izuku nervously laughed as he slipped his phone into his pocket. The world of Quirks was certainly a weird one. And Izuku was sure this wasn't going to be last time that something like this was going to happen again.


	2. Hopping Catastrophe

(A/N): Alrighty the premise of this next "side effect" drabble is of Bakugou and Midoriya getting turned into animals! Hope you enjoy!

* * *

Katsuki was so going to kill someone. One minute he was readying himself for school and in a puff of smoke he was much smaller and buried in his own clothes. As soon as he crawled out of the pile of cloth Katsuki made sure to check himself over. He wasn't just shrunken down, no, he wasn't even human anymore.

 _Oh hell no!_ He hissed, very literally hissed. He was a cat. A cute little ball of puffed up fur cat. He had no idea what he was to do. But then he remembered something from the day before. He wasn't the only person that had helped deal with a random villain the other day.

 _Deku…fuck._ Katsuki huffed as he realized that the other boy could also be in this type of situation. He really did not want to deal with his "rival" but he still knew he had to do something about all this. Thankful that he had left his bedroom window open, Katsuki, though through a couple of stumbles, made his way up and out. As he wandered the sidewalk Katsuki sort of enjoyed this whole cat thing. For the most part he was getting ignored and he was very light on his feet. The world had all kinds of smells he never knew before and the whole cat-sight was an experience. The blond was making good time to U.A. and was proud of himself; tail flagged high at the fact. That was until something caught his eye and sudden urges came over him. Something small was quivering in some bushes. Katsuki ducked low and crept towards the bush. Claws slowly slipped out of Katsuki's paws and inside his head he was a tad conflicted. He didn't want to succumb to kitty desires, but this also felt so right. Just as Katsuki was to pounce the object of his fixation was suddenly scooped but by human hands.

"Oh no kitty, you aren't eating Mr. Bunny." Katsuki recognized the U.A. uniform, but he had no clue who it was he was looking at. Gravity-Defying purple hair and tired eyes looked right the catified-human along with a strong smell of coffee in the air. After deciding he didn't care about the person Katsuki looked to his previous prey. In the human's hands was a green-furred rabbit that was shaking like a leaf. Something seemed oddly familiar about the rabbit and it pissed Katsuki off.

"Now then what are you two doing out here?" The human tucked the rabbit under his arm and knelt down closer to Katsuki. With a free hand the human held it out the the feline. Katsuki hissed at the human. He wasn't some stray cat to get coddled!

"Angry little thing eh?" The human rolled his eyes and stood back on his feet. He then turned to the rabbit under his armpit. The rabbit made a pathetic squeak and shook just a little less. "Well at least this guy accepts a helping hand." The human turns his back to the cat and starts to leave.

 _Good fucking riddance. Guy had shittier hair than Kirishima._ Katsuki sticks his little pink nose in the air and continues on his journey to inside the school. Glad that the hallways weren't crowded Katsuki made his way to class 1-A. Taking a peak inside he tried to spot Izuku.

"I haven't heard from Midoriya since yesterday. It's not like him to not come to class." It was good-ol' Half and Half that was talking.

"I hope he's okay. He was in that fight yesterday after all. Say Kirishima have you heard from Bakugou?" It was Ochako that was speaking this time.

"Nah, normally when I bug him with as many texts as I have he curses me out to leave him be." Eijirou shakes his head and pouts. Katsuki can feel his fur start to stand on end. Great now whenever he's back to normal he's going to have to deal with the red-head's whines and ridiculous emojis. However, as the others' words start to sink in Katsuki realizes something. He was turned into a cat, Deku was missing, and he and Deku both were involved in the attack the other day.

 _That fucking rabbit!_ A lightbulb goes off in Katsuki's head as the pieces all fit together. He needed to go find shitty hair 2.0. The little blond cat is soon skittering across the U.A. hall tiles as he goes to look for the purple-haired background character. When a recognizable coffee scent fills Katsuki's nose he knows just where to go. He ends up in the General Studies area of U.A. and Katsuki can't seem to find the words to describe the fact that he had to wander here. But to the most of the blond's surprise he didn't have to invade a classroom. Instead, in a Aizawa-like manner, Katsuki finds the human of his hunt dozing up against a vending machine.

 _What the fuck are you doing out here?_ Katsuki rumbles as he gets closer to the person. _You should be in class shithead!_ An eye cracks open and a smile finds its way to the human's face.

"Hello again kitty-cat."

 _Where'd you put that rabbit-Deku?!_ Katsuki wants to speak but all that comes out of his mouth is mewls. The human only chuckles and goes to run a hand down Katsuki's back. _Dammit that felt nice._

"This is no place for you. Come here." Before Katsuki could realize what was going on, he was up in the human's arms.

 _Let me go fucker!_ Katsuki yowls and sinks his teeth into the human's hand. But the human only laughs.

"What a wild thing you are…you remind me of a certain someone from the Sports Festival."

 _The sports festival? Wait a minute…You!_ Katsuki let's go of hand; he finally recalls who this person is. The brainwasher that almost pathetically whipped Deku's butt. _What was his name again? Shin-something._ Katsuki rumbles as he thinks.

"Say, can you promise me not to attack the bunny again? The two of you are going to have to share a space again for a little bit. Cause I doubt you want to be around here like you currently are." Shin-whatvever rambles as he heads to the dormitories that aren't too far from the school itself.

 _This little shit already rooms at the school?_ Katsuki looks up to Shin curiously. But it appears the human is no longer in a talking mood. He simply hums as he continues into the dormitory. Once into a room, of which Katsuki can only assume is Shin's own, he is finally let down. Feet back on the ground he trots away from Shin only to turn and glare at the person.

 _Where's Deku?_ He meows.

"Hungry? I don't really have anything cat-safe for you right now." Shin takes a hand and rubs at the back of his head.

 _No! I need to see if that stupid rabbit is Deku!_ Katsuki hisses.

"Geez, not one for taking apologizes?" Shin chuckles and walks by petting Katsuki as he goes. Rolling his eyes, or at least thinking he is, Katsuki wanders off to search for the green bunny. He comes across the fluffy bun quiet easily and has to jump a desk to come to him. The rabbit's eyes grow wide as he stares at the incoming predator.

 _Now then are you Deku or just some random fucking rabbit?_ Katsuki meows at the bun not sure if he can even understand him. The rabbit jumps and after spinning in confusion, hops off the desk and runs for it. _Fuck you!_ Katsuki gives chase; which probably wasn't his best idea.

"You piece of shit." Katsuki is scooped up after he runs by Shin. "I said not to chase the fucking rabbit." Katsuki only gives the other a bored glare. By now the rabbit was huddled up in a corner heavily breathing.

 _Not my fault he won't stay still enough to talk to me!_ Katsuki huffs.

"I think you need a cat nap…I know I do." Shin sighed and despite the last part being whispered, Katsuki heard it perfectly fine. Shin heads to a bed and plops right down, making sure to let Katsuki free onto the mattress as he did so. Said yellow cat couldn't help but jump slightly as the mattress moves when Shin lays back onto the bed; evidently passed out.

 _Does this dumbass not sleep regularly?_ Katsuki can't believe that he's now caught this person asleep twice. Sighing to himself Katsuki curls up next to the human; there's not much he can do until the rabbit calms back down and honestly, a nap sounded nice. As he closes his eyes he can feel a hand sudden go across his flank.

"What a good kitty…" Deciding not to care for now, Katsuki let's the petting happen with no fuss on his end.

 _K…Kacchan?_ Katsuki perks up at the call of that horrid nickname of Deku's.

 _So you are indeed Deku._ He huffs as he adjusts himself to spy the rabbit while staying curled in the bed.

 _You're being awfully nice to Shinso._ Izuku hops a bit closer to the bed.

 _Is that his name?_ Katsuki shakes his head, _Whatever, why the fuck did you keep running from me?_

 _How was I supposed to know it was you? I thought you were going to eat me!_ Izuku actually makes some kind of noise as he perks his ears.

 _I should have if you're going to keep whining._ Katsuki's ears pull back as he snarls.

 _Kacchan!_ Deku spins in a circle as he squeaks.

 _Guess now that I've found you we should go find Recovery Girl or something._ Katsuki seems to sigh as he stands and stretches.

 _But how will we let her know it's us? Same can be said if we try to see if Mr. Aizawa can cancel this Quirk effect._ Deku flops onto his side as he seems to be worn out.

 _Better than staying here and becoming this guy's pets._ Katsuki claims as he comes down from the bed.

 _You didn't seem too adverse from the idea._ Izuku comments and is quick to dodge a swipe from a fluffed up Katsuki.

 _Let's go._ Katsuki sternly states and starts to head to the door. The two turned-animals carefully make their ways out of the dorm room and dormitory altogether. They go through a few verbal spites as they make it into the main U.A. building.

 _We are so lucky that we're wandering the halls when nobody is around._ Izuku comments as he and Katsuki are almost to Recovery Girl's.

 _Don't count your blessing too soon. Idiot._ Katsuki huffs in response.

"Oh what's this? Where'd you come from. That and a rabbit and cat so close together and not fighting?" Both Izuku and Katsuki turn around to see Principal Nedzu. The pair can only give their Principal a deer-in-the-headlights look.

 _What should we do Kacchan?_ Izuku asks with his ears flopping down.

 _How the fuck should I know?_ Katsuki returns with a hiss.

"Ah I thought you two looked familiar. Now Mr. Bakugou please try and control that language of yours." The Principal wags a finger at the cat and bunny.

 _Guess he can understand us._ Izuku points out.

 _Obviously!_ Katsuki huffs. Principal Nedzu proceeds to grab the pair and walk them to Recovery Girl's. While doing so he makes a call for Mr. Aizawa to meet him there. Soon enough the two boys are back to their human selves (and put in some replacement uniforms one would add). The day is then treated as if the pair was sick at home for the school day and would be back into the normal swing of things the following day. Though when said day comes by, Katsuki makes a small detour on the way to class. He finds a sleepy purple-haired peer out on a bench by a training yard and leaves a thermos of coffee by his backpack.

"…Thanks, I guess." Katsuki quietly states as he leaves. But little did he know, Shinso wasn't completely asleep.

"I wonder what that was about…" Shinso grins as he takes a sip from the thermos the U.A. asshole has left him. "Damn that's good stuff. What a good little kitty." His snickers are thankfully heard by no one.


End file.
